(M1430-04-21) Comparison of the Tendency of DC Excipients to Build-Up of Static Electricity

Purpose: Accumulation of electrostatic charges is a common problem occurring during processing of powders in in the production of solid pharmaceutical dosage forms. The problem appears through e.g., sticking of electrostatically charged particles to the processor walls and can hinder stable powder processing. For this reason, the usage of components with a low tendency to build up static charges is very advantageous in powder mixtures. The aim of this study was to evaluate and compare the tendency of various directly compressible (DC) pharmaceutical excipients to accumulate electrostatic charges.

Methods: A JCI 150 Faraday Pail (UNITOR s.c., Torun, Poland) was used to measure the electrostatic charge of the powder blends. The samples and mixing equipment were discharged with a U-Electrode (Mettler-Toledo GmbH, Giessen, Germany) before every single measurement. 5 g of each material was placed in a 100 mL borosilicate glass 3.3 vessel, mixed for 100 s at 32 rpm in a Turbula^® mixer (Willy A. Bachofen AG, Muttenz, Switzerland), and transferred into the Faraday Cup. The charge density (q) was calculated by dividing the measured electrical charge by the sample mass. Additionally, the particle size distribution of the excipients was measured with a CAMSIZER X2 (Microtrac Retsch GmbH, Haan, Germany) dynamic image analysis device. All measurements have been done in triplicate at dry mode with a dispersion pressure of 1 bar.

Results: Figure 1 shows the comparison of accumulated charge density after mixing in a glass vessel. Materials were grouped by chemical identity and ordered according to their particle size. The electrostatic charge was generated through friction and collision of the particles between themselves and the wall of the vessel during the mixing process. The tendency to accumulate electrostatic charge was influenced by both the chemical identity of the excipient and its particle size. Smaller particles of the same substance had a greater tendency to build up static electricity. This was due to the increasing corresponding specific surface area of powders. Of the anhydrous substances, fillers based on calcium phosphates showed lower tendency to build up static electricity. The most problematic with this respect was anhydrous lactose with median particle size of around 100 µm. Of the substances containing larger amounts of moisture, microcrystalline cellulose accumulates the largest amount of static electricity.

Conclusion: In this study, the tendency of common DC excipients to build-up electrostatic charges was compared. It was found that excipient based on dibasic calcium phosphates had a smaller tendency to accumulate electrostatic charges compared to other tested material, i.e. lactose and microcrystalline cellulose.

References: 1. Rescaglio, A.; De Smet, F.; Aerts, L.; Lumay, G. Tribo-electrification of pharmaceutical powder blends. Particulate Science and Technology. 37(8), 1024-1031 (2019).
2. Sahu, R. Handling static charge at pharmaceutical manufacturing. Express Pharma. 10(3), 80-2 (2014);

Table 1. Particle size distribution of selected DC excipients.



Figure 1. Electrostatic charges accumulated by selected DC excipients